import java.util.*;





public class Solution3 {
    public class ListNode {
    int val;
    ListNode next = null;
}
    /**
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode deleteDuplicates (ListNode head) {
        // write code here
        if(head==null){
            return null;
        }
        ListNode cur=head;
        while(cur!=null&&cur.next!=null){
            if(cur.val==cur.next.val){
                cur.next=cur.next.next;

            }
            else{
                cur=cur.next;
            }
           
        }return head;
    } 
}